Forensic DNA Profiling and Biological Evidence (STR, Mitochondrial DNA, Paternity, Kinship) MCQs

Forensic Medicine · 23 free questions with answers & explanations.

1. In forensic STR profiling, a suspect's DNA sample shows two alleles at a locus (heterozygous), but the crime scene sample shows only one allele at the same locus that does not match either of the suspect's alleles. What is the MOST appropriate interpretation?
2. Mitochondrial DNA (mtDNA) analysis is preferred over nuclear STR typing in which of the following forensic scenarios?
3. In a disputed paternity case, the alleged father's STR profile shares alleles with the child at 12 out of 13 loci tested. At the 13th locus the child carries an allele not present in either the mother or the alleged father. What is the most likely explanation?
4. Y-chromosome STR haplotyping is unique among forensic DNA methods because it:
5. A forensic DNA laboratory reports a mixture ratio of 1:9 (minor:major contributor) in a sexual assault case. The analyst wishes to extract only the spermatozoa fraction for STR profiling. Which extraction method selectively lyses epithelial cells first while leaving sperm cells intact?
6. A forensic scientist receives a degraded bone sample from a mass disaster. Autosomal STR profiling fails due to degradation. The preferred next-step molecular technique to attempt identification by maternal lineage comparison is:
7. In forensic DNA databasing under CODIS (Combined DNA Index System), the minimum number of STR loci in the current expanded core loci panel used for profile comparison is:
8. Familial DNA searching in forensic databases identifies a partial match to a crime scene profile. The database hit belongs to a convicted offender's sibling, not the offender himself. The probability that the crime scene profile belongs to a full sibling of the database entrant compared to an unrelated individual is approximately:
9. A forensic laboratory is comparing two STR profiles from a crime scene. The suspect's profile shows alleles 14,17 at locus D3S1358 and the evidence shows 14,17 at the same locus. The probability of this match occurring by chance in the relevant population is 1 in 1,200,000. This value is best described as:
10. Mitochondrial DNA (mtDNA) analysis is preferred over nuclear STR profiling for forensic identification in which of the following scenarios?
11. In forensic paternity testing, an alleged father shows a genotype of 12,15 at a microsatellite locus; the child is 15,18 and the mother is 12,18. Which statement correctly interprets the genetic evidence?
12. Y-STR analysis in forensic science is MOST useful in which of the following situations?
13. Which of the following DNA markers has the LOWEST discriminating power and is therefore NOT suitable as the sole basis for individual identification in forensic casework?
14. In forensic DNA profiling using short tandem repeats (STR), the CODIS database in the US uses how many loci for the expanded CODIS core, and what is the primary advantage of increasing loci from 13 to 20?
15. A decomposed body is recovered from a river after 3 months. Nuclear DNA is severely degraded. The most appropriate DNA source for identification in this scenario is:
16. In a paternity dispute, the Paternity Index (PI) of a particular STR marker is 15. The Combined Paternity Index (CPI) calculated from 10 independent loci is 2,500,000. What is the correct interpretation?
17. A forensic biologist identifies touch DNA on a weapon handle recovered from a crime scene. The principal limitation of touch DNA (low copy number DNA) analysis compared to standard STR profiling is:
18. Familial DNA searching in a forensic database identifies a partial STR match to an uploaded crime scene profile. This technique is BEST described as:
19. In a paternity dispute, the alleged father is unavailable for testing. DNA profiling using autosomal STR markers is performed on the child, the mother, and the paternal grandfather. Which genetic principle allows kinship inference in this scenario?
20. A forensic lab receives a degraded skeletal remain from a mass disaster. Standard autosomal STR profiling fails due to low template quality. Which DNA strategy offers the highest probability of obtaining a profile from severely degraded bone?
21. The Likelihood Ratio (LR) in forensic DNA evidence interpretation is defined as the probability of the evidence given the prosecution hypothesis divided by the probability of the evidence given the defence hypothesis. An LR of 1 000 000 means:
22. In a rape case, vaginal swabs are collected. The DNA analyst reports a 'mixed profile' with at least three contributors. The major contributor matches the husband; a minor contributor has a partial profile. Which forensic interpretation challenge is MOST significant?
23. A forensic case involves a hair shaft without the root. Which type of DNA analysis is MOST appropriate, and what is its key limitation compared to nuclear STR profiling?